Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of acetic acid and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. Depending largely on manufacturing method, different commercially available acetic acid compositions contain differing levels and types of impurities. The presence of these impurities may negatively impact catalyst performance and lifetime in the catalytic reduction of acetic acid to ethanol.
In addition, the corrosive nature of acetic acid, particularly in liquid form, may cause the leaching of corrosion metals from processing conduits, reactors, and other vessels in reaction systems involving acetic acid. Such metals may also detrimentally impact catalyst performance and lifetime in reaction systems employing acetic acid, necessitating the lining of such engineering equipment with materials resistant to metal leaching and resulting in significant capital cost.
For the foregoing reasons, the need exists for new and improved processes for removing impurities from acetic acid, and in particular to removing impurities from acetic acid that is used in reaction systems for catalytically reducing acetic acid to form salable ethanol.
The need remains for ethanol production processes for removing impurities within the hydrogenation system.